Algebraic method

[kathy's]

I don't know were to begin
I have to solve this question by using algebraic method:

1) 3x= -12
2) 1= x+y+2z
3) 2x-y= -9
can you help me?
Thanks

 

[Denis]

1) 3x= -12
2) 1= x+y+2z
3) 2x-y= -9

Hmmm...looks familiar...anyway:
1): x = -12/3 = -4 ; ok?

Substitute that in 3):
3): 2(-4) - y = -9
y = 1 ; ok?

Now finish off by substituting x=-4 and y=1 in 2);
if you can't, you need more help than you can get here...your teacher :!: